This invention relates to a drive system for road vehicles, in particular public transportation and semitrailer vehicles.
Several hydrodynamic or oil-operated drive systems are currently known and marketed, all such systems being referred to hereinafter as "hydraulic drive systems", as known are advantages afforded thereby. For transmitting motive power on transportation vehicles, such hydraulic drive systems have gained acceptance mainly on account of their inherent ability to provide a continuously variable drive ratio and independent control of the speed and torque delivered to each driving wheel. To accomplish the former goal, hydraulically operated units have been developed for installation in lieu of the clutch/transmission assembly employed in traditional drives. The latter goal is instead achieved by providing a pump to feed a number of hydraulic motors, each motor being coupled to one wheel of the vehicle.
While the former systems is mainly directed to making the driving of the vehicle more convenient, as an alternative to fully automated transmissions, the latter has substantial advantages from the standpoint of engineering and economy, and is generally preferred for industrial vehicles. Moreover, the latter system affords the additional advantage of eliminating the need for differential gears and driveshafts, such that, at least in principle, it may be reduced to but one pump and two or four hydraulic motors.
However, traditional power drive systems have been definitely improved through the years, especially as relates to automatic transmissions and differential gears. Thus, the technical problem arises of investigating whether novel and particularly advantageous combinations may be found among the hydraulic drive units and mechanical drive units.